Instrument for measuring the carbon content of steel



Dec. 9, 1952 R. c. BUEHL 2,621,234

INSTRUMENT FOR MEASURING THE CARBON CONTENT OF STEEL Filed June 25, 1951 Pussa L C. BUEHL Patented Dec. 9, 1 952 UNITED STATES PATENT DFFICE JNSTRUMENnFoR MEASURING THE .oAnBoN .QONTENT or STEEL Russell Q'Buelilyllittsburgh, Pa, assignor to the 'United'States of America as represented bythe Solicitor of the Department of the Interior Applica ionafia 1951, Se a 33,478

(Granted-under the act of March 3, 1 883, as amended April 30, 1928; 3'70 0. G. 757) 4 Claims.

(3.90% carbon. Duringtherefining of steel, that is, when --steel exists as liquid rnetal in -open hearth or electric furnaces, the carbon content can change rapidly. The anlysis of samples-0f --metals from the bath by chemical methods is often too slow, that is, the carbon content of the bath will change appreciably before the-analysis can be completed. For this reason, instrumentshave been developed for estimating-the carbon contentofa bathby means ofphysical measurementson cast specimens, that is, measurement of magnetic properties orhardness.

Such instruments in the past have beenex- -pensive to construct and difiicult to fabricate,

calibrate, and utilize. These instruments usually contain a meter which must be interpreted by reading the maximum deflection of a-swinging instrument pointer or by taking an average-reading-of an oscillatingpointer. 'In addition-instruments in the past "hav required either batteries or an outside source of electrical power. The calibrationof these-instruments has been difficult and normally the calibration is-seriously affected by changes in temperature and humidity.

An object of this invention .is to provide an instrument formeasuring the carbon content of steel which is cheaper to construct, more reliable and easierto use than present instruments.

A further objeotof the invention is @to provide an instrument which gives a constant meter reading rather than requiringareadin fromnn oscillating meter pointer.

It is an additional objectof the invention to provide an instrument which requires no batteries or outside connections to ,a source of electrical power.

Another object of the invention is to provide an instrument which may be easily calibratedand will retain constant calibrationfora long period of time.

Arn t wl objec of the i v nti n i a rmd e er in w s hefi u a he ride an instrumen wherein th path a l es lieznends upon the stren t .bf

g ts d a coil spring and is not'afiected by peratu e an hum dity.

Other o j s and advantagesil merri 9i i s r m a a eful c n id atiqzl a embodimen of he--inventiQI -'=l e c he e in of is pp ationwhe iem The figure is an isometric view, partially 7331113 Way, of a m t me ephedrine m tionin a a t cu a emb d men gf th inven n.

a casinglfl which serves as .the-cas ejcon the remainder of the instrument and also serves as part of the magnetic circuit of the instrument as will hereinafter be more particularly described. Case Hl ispreferably made of steel, but .any'magnetic material may be used. This metal box i0 also serves to shield the instrument from ,the effects of extraneous magneticfieldsorthe presence of pieces of iron, such as tools, outsidethe instrument, the advisability of which is apparent from the opertaion of the deviceashereinafter described.

Bositioned in case it is .a meter L! whichis supported with the meterface formingpartof the surface of easing It. The details of themeter will be described hereinafter. The casing III also contains an opening [2 in another wall thereof.

This opening serves to allow the sample .Sto-be tested to be inserted in the instrument. Positioned in the casing IE1 and properlyaligned with opening I2 is cone-Shaped piece 13 preferably formed of magnetic material which serves to shield the meter from the magnetic properties of the head of a specimen S being tested as will more particularly be described hereinafter. Shield 13 is indirectly supported .by Casing I0 through a supporting member I l which isformed of a non-magnetic material.

Positioned in thecase .lll is an assembly for supporting a magnet 15, andfor formin apart of a circuit for the magnetic flux of the magnet I5. This assembly comprises themagnet 1,15 itself which is mounted for rotation on, a shaft -I6,Ione end of which extends outthrough casing. and terminates inknob H. Thev onpositeend tthe shaft I6 is provided with an arm 18 whichlcOoperates with a fiexiblepiece H1 whiGh-containsa slot wherein arm i8 may-be positioned, to maintain the magnet It in :a vertical position. The assembly also contains pole pieces-20 and 2 Iwhich are shown in the f gure as beingrespectively below and above themagnet I-5. TheSepolepides 20 and 2| are preferably formed of soft iron and are supported in their respective positions by members 22 and 22 which are formed of a nonmagnetic, insulating material. A screw 23 is mounted on the upper pole piece 2|. This screw may be adjusted to change the effective strength of magnet l by short circuiting a part of the magnet flux from magnet M5 to case Ill. Lower pole piece 20 contains an opening 24 which opening is aligned with that in shield 53 and is used to support the sample S which is to be tested.

Meter II, as shown in the figure, is composed of a stationary vane 30 which is formed of magnetic material, preferably soft iron, and a similar movable vane 3|. Movable vane 3| is fixedly mounted on a shaft 32 which is supported in the meter by pivots such as 33. The pointer 34 of the meter is fixed to shaft 32. A coil spring 35 is also fixed to shaft 32 and to piece 36 which is attached to the meter face. The coil spring 35 serves to return the pointer 34 to a fixed position when no sample is being tested as will hereinafter be described.

Mounted below the meter I l is a suitably shaped pole piece of magnetic material 31, preferably "soft iron, in which is drilled a hole 38 into which the end of the sample S may be positioned.

As is obvious from a consideration of the figure,

hole 38, hole 24 and the hole in shield (3 are all aligned in order to allow insertion of the sample S into the instrument. These holes are of a sumci'ent size to allow the insertion of the sample, but are kept to tolerances which minimize the clearance between the sample and the elements 31, 29,

and 13 as much as practically possible.

A magnet 39 is also positioned in the case It "and is positioned on the opposite side of pole piece 31 and meter l I from magnet l5. This magnet 39 is used to compensate for the deflection of the meter due to magnet when there is no sample S in the instrument.

The instrument of the invention as above described and as shown in the figure operates in the following manner. The permanent magnet 15 provides the constant magnetic field which serves j sorted into the instrument through shield l3, hole 24 and into hole 38 in pole piece 37. The sample as cast usually has a cone-shaped head portion due to the shape of the casting mold and shield I3 is formed in such a shape, as shown, in order to allow for this head portion.

The magnetic flux of magnet l5 follows a closed path and causes the meter to register. The flux follows a path from the magnet I5 through the soft iron pole piece 20, through sample S, through pole piece 31, across a small air gap, through vanes 30 and 3| in parallel, across a second air gap, through the metal case it) and through pole piece 2| to the other end of magnet l5.

Assuming that magnet l5 has a north pole pointing downward, the vanes 30 and 3! would be magnetized with a north pole at the top and a south pole at the bottom. Since similar magnetic poles repel, the movable vane 3| will move "away from the fixed vane 30 until the magnetic force is balanced by the restoring force of the spring 35, thus deflecting pointer F. It is obvious that this movement is directly related to the magnetic properties of the sample S, which is part of the close circuit for the flux.

In order to obtain a magnetic flux in the sample which is independent of possible previous retained magnetlsm in the sample, magnet I5 is rotated by means of shalt lb so that the flux in the sample S is reversed several times prior to a reading. When steels are magnetized, they retain a certain amount of permanent magnetism and will not reach zero magnetism until a small magnetizing field is applied in the reverse direction (phenomenon called hysteresis). Ir an unmagnetlzed sample is magnetized then the magnetic field removed and reapplied, the magnetic flux in the sample will be slightly higher at the same field strength than during the first application of the field. However, if the field is reversed several times a value of magnetic flux is reached for a given field strength aiter which further reversals have no eiiect on the relation of magnetic Iiux to field strength. Consequently, the deflection or the meter would then depend only on the magnetic properties of the sample S and would be independent of whether it had been magnetized prelarge portion of the magnetic flux from magnet l5 would proceed through the pole piece 20, sample S, shield 13 then through the casing ii] to pole piece 21 and back to magnet Hi. This would obviously reduce the magnetic field available for deflecting meter H.

Compensating magnet 39 increases the accuracy of the meter by spreading the useful range of the meter by its action of compensating for the deflection of the meter due to magnet l5 when no sample is in the instrument. If magnet 39 is not present in the devlce, the meter will be deflected and the range of the meter will be from this point to the extent of the meter scale. When this compensating magnet is present, the meter justed as to overcompensate the field of the magnet l5, that is, to produce some deflection on the instrument such as two divisions without any specimen (full-scale deflection is taken as ten divisions). A cast specimen is then inserted into the instrument and as the specimen approaches the piece 31 the pointer 34 will first move toward zero and then again move up scale. The position of the stationary end of the hair spring 35 is set by means of the meter adjustment screw so that this minimum reading will correspond with zero on the scale. A piece of low carbon steel which is used as a standard of calibration is next inserted in the instrument and the magnet l5 rotated several revolutions by means of the knob I! to eliminate hysteresis in the calibration sample and other metal parts. Magnet I5 is then returned to its vertical position and held in place by the spring member 19. The meter reading is admagnet in its vertical position. The carbon content of the cast specimen is then determined by analysis and a calibration chart prepared showing the variation of carbon content with meter readings. By then following a similar procedure of casting, quenching, and reading, the carbon content of the steel bath can be determined from the meter reading on the instrument.

It should be appreciated that the shape of the calibration curve of carbon content versus meter reading can be varied by altering the size, shape and location of pole piece 31 and by changing the shape of vanes 30 and 31.. The vanes can be made of triangular pieces of soft iron rolled into cylinders of different diameters with the movable cylinder inside the stationary cylinder. In addition, one of the vanes can be made of a hard, permanent magnet material so that it would not become demagnetized by the field of the other magnets.

It should be appreciated that the instrument of this invention has other uses than the determination of the carbon content in steel. Any variable characteristic of the sample which will alter its magnetic properties may be measured by this instrument. The device may, therefore, be used to determine some magnetic property of steel used as a magnetic material, to measure the depth of a hardened case on a steel bar, to determine the hardenability of steel, that is, the depth to which it will harden by quenching, and other uses which are obvious from a consideration of this application.

It will be appreciated from a reading of the foregoing specification that the invention herein described is susceptible of various changes and modifications without departing from the spirit and scope thereof. The invention is, therefore, to be limited only by the scope and spirit as set forth in the appended claims.

What is claimed is:

1. An instrument for measuring the magnetic properties of a sample of metal which comprises a steel case, a permanent magnet positioned vertically in said case, said magnet mounted on a rotatable shaft supported horizontally by said case, a plurality of soft iron pole pieces mounted respectively above and below said magnet and positioned by a plurality of supports formed of nonmagnetic insulating material, said lower pole piece having an opening therein wherein a portion of said sample to be tested may be positioned, a variable screw connecting said upper pole piece to said case, a meter mounted in and supported by said case, said meter comprising a fixed vane and a vane fixed to a shaft which is rotatable and has connected thereto a meter pointer, said vanes being formed of soft iron, a pole piece extending from the lower portion of said meter, said pole piece having an opening wherein an end of said sample may be positioned, an opening in said case through which said sample may be passed, said opening in said case and openings in said pole pieces being aligned to accommodate said sample, and a second magnet in said case positioned on the side of said meter opposite to said first magnet to thereby serve as a compensating magnet.

' 2. An instrument for measuring the magnetic properties of a sample of metal which comprises a case formed of magnetic material, a magnet mounted in said case, said magnet being mounted on a rotatable shaft supported by said case, a plurality of pole pieces formed of magnetic material mounted at the extremities of said magnet, an opening in one of said pole pieces, a meter mounted in said case, said meter comprising a fixed vane and a movable vane which is fixed to a meter pointer, said vanes bein formed of mag netic material, a pole piece formed of magnetic material extending from said meter, an opening in said pole piece wherein an end of said sample may be positioned, an opening in said case through which said sample may be passed, said opening in said case, and said openings in said pole pieces being aligned to accommodate said sample, and a second magnet in said case positioned on the side of said meter opposite to said first magnet to thereby serve as a compensating magnet.

3. An instrument for measuring the magnetic properties of a sample of metal which comprises a case, a magnet mounted in said case, a pole piece mounted at an extremity of said magnet, an opening in said pole piece, a meter mounted in said case, said meter comprising a fixed vane and a movable vane which is fixed to a meter pointer, a pole piece extending from said meter, an opening in said pole piece, an opening in said case through which said sample may be passed, said openin in said case and said openings in said pole pieces being aligned to accommodate said sample, and a second magnet in said case positioned on the side of said meter opposite to said first magnet to compensate for said first magnet.

4. An instrument for measuring the magnetic properties of a sample of metal which comprises a case, a magnet mounted in said case, a pole piece mounted at an extremity of said magnet, an opening in said pole piece, a meter mounted in said case, said meter bein operable to register magnetic flux, a pole piece extending from said meter, an opening in said pole piece, and an opening in said case through which said sample may be passed, said openings in said case and said pole pieces being aligned to accommodate said sample.

RUSSELL C. BUEHL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 508,827 Knap et al. Nov. 14, 1893 1,682,435 Spooner Aug. 28, 1928 2,384,529 Breitenstein Sept. 11, 1945 

1. AN INSTRUMENT FOR MEASURING THE MAGNETIC PROPERTIES OF A SAMPLE OF METAL WHICH COMPRISES A STEEL CASE, A PERMANENT MAGNET POSITIONED VERTICALLY IN SAID CASE, SAID MAGNET MOUNTED ON A ROTATABLE SHAFT SUPPORTED HORIZONTALLY BY SAID CASE, A PLURALITY OF SOFT IRON POLE PIECES MOUNTED RESPECTIVELY ABOVE AND BELOW SAID MAGNET AND POSITIONED BY A PLURALITY OF SUPPORTS FORMED OF NONMAGNETIC INSULATING MATERIAL, SAID LOWER POLE PIECE HAVING AN OPENING THEREIN WHEREIN A PORTION OF SAID SAMPLE TO BE TESTED MAY BE POSITIONED, A VARIABLE SCREW CONNECTING SAID UPPER POLE PIECE TO SAID CASE, A METER MOUNTED IN AND SUPPORTED BY SAID CASE, SAID METER COMPRISING A FIXED VANE AND A VANE FIXED TO A SHAFT WHICH IS ROTATABLE AND HAS CONNECTED THERETO A METER POINTER, SAID VANES BEING FORMED OF SOFT IRON, A POLE PIECE EXTENDING FROM THE LOWER PORTION OF SAID METER, SAID POLE PIECE HAVING AN OPENING WHEREIN AN END OF SAID SAMPLE MAY BE POSITIONED, AN OPENING IN SAID CASE THROUGH WHICH SAID SAMPLE MAY BE PASSED, SAID OPENING IN SAID CASE AND OPENINGS IN SAID POLE PIECES BEING ALIGNED TO ACCOMMODATE SAID SAMPLE, AND A SECOND MAGNET IN SAID CASE POSITIONED ON THE SIDE OF SAID METER OPPOSITE TO SAID FIRST MAGNET TO THEREBY SERVE AS A COMPENSATING MAGNET. 